From DE 37 11 013 C1 a pedicle screw for stabilizing spinal column segments is known, in which the screw element is articulatedly connected to a receiver part. The receiver part comprises two halves surrounding the head of the screw element and a guard ring holding them together. The receiver part further has receiving slits for inserting a threaded rod. Locking the head in the receiver part and fixing the threaded rod is done by nut-shaped fixing screws screwed on to the threaded rod on both sides of the receiver part, which fixing screws act laterally on the receiver part.
A bone anchoring device according to the preamble of patent claim 2 and a receiver part according to the preamble of patent claim 1 are known form DE 39 23 996 C2. In the known device, to fix the angle of the bone screw relative to the receiver part, a pressure element acting on the head of the bone screw is provided. Fixing the rod, constructed as a threaded rod, takes place by means of nuts screwed on to the rod, which act laterally on the receiver part. In the assembled state a force is exerted on the head in the axial direction of the receiver part via the pressure element in such a way that the head is locked in the receiver part.
A bone anchoring device according to the preamble of patent claim 2 and a receiver part according to the preamble of patent claim 1 in which there is a pressure element for fixing the head are also known from DE 43 07 576 C1. Fixing the head and rod takes place by means of a fixing screw which can be screwed into the receiver part and a lock nut screwed on to the receiver part, which exert a force on the pressure element in the axial direction of the receiver part.
In the U.S. Pat. No. 5,728,098, a bone anchoring device according to the preamble of claim 2 and a receiver part according to the preamble of claim 1 are described. Head and rod are fixed separately by two rings of memory shape alloy. For this purpose, the receiver part has a pair of opposite upper slots and a pair of opposite lower slots. Receiver part, screw and lower ring are pre-assembled loosely, and in this state, the bone anchoring device is screwed into the bone. Thereafter the rod is inserted and the upper ring is mounted. By the temperature of the body the two memory shape alloy rings contract. Thus, head and rod can be fixed separately in the receiver part by the two corresponding rings.